Decomposition differences between snags and logs in forests of Kenai Peninsula, Alaska

Abstract

Rising temperatures could increase forest ecosystem disturbance frequency and severity, transferring large amounts of live biomass to coarse woody debris (CWD) pools that emit carbon (C). The type of disturbance-created CWD influences the rate, amount, and duration of this C emission. We studied the effect of a large-scale disturbance on CWD dynamics in spruce-dominated forests of the Kenai Peninsula, Alaska, by determining CWD decomposition rate constants (k) using the chronosequence and decomposition-vectors methods and by modeling the hypothetical CWD dynamics occurring after a bark beetle outbreak versus a windthrow. Chronosequence-based k’s for mass ranged between 0.020 and 0.022 year−1 for logs and between 0.000 and 0.003 year−1 for snags. Decomposition-vectors-based k’s for log mass ranged between 0.022 and 0.045 year−1 among three decomposition phases and between 0.014 and 0.048 year−1 among five decay classes. Our analysis showed that snag-generating disturbances delayed C flux from CWD to the atmosphere, produced a smaller magnitude of C flux, and had the potential to store 10% to 66% more C in the system over time than disturbances generating logs. Thus, landscapes affected by disturbances creating snags (versus logs) may revert faster to C neutrality, suggesting forest management practices should reflect these differences.